The present invention pertains to the production of composite corrugated webs, such as paperboard, and more particularly to the production of double wall corrugated paperboard web in which the flutes of the corrugated medium webs are synchronized and aligned flute-to-flute.
Single wall and double wall corrugated paperboard webs have traditionally been made in a corrugator utilizing, respectively, a basic two stage and three stage process. For single wall board, a single face web, comprising a corrugated medium web and a liner web, are formed in a single facer. In the second stage, the single face web is transferred to a double backer where a second liner web is glued to the exposed corrugated medium web flute tips of the single face web and is passed through a heating section to cure the adhesive and complete the single wall web. Production of conventional double wall corrugated board typically utilizes a second intermediate single facer to produce another single face web in a second stage of the production process. In the third stage, the second single face web is adhesively attached by its liner web to the exposed glued flute tips of the first single face web and, simultaneously, the final (usually lower) liner web is brought into contact with the exposed glued flute tips of the second single face web, and the assembled webs are transported through the heating section of a double backer to provide a final adhesive cure and form the double wall corrugated web.
Typically, in the manufacture of double wall corrugated board, the two single face webs are joined without regard to alignment or synchronization between the flutes in the corrugated media of the two webs. Indeed, often the two single facers produce corrugated webs in which the pitch length of the flutes is different and, therefore, no alignment or synchronization is possible.
However, another type of double wall corrugated web is produced in which the intermediate liner web is eliminated, the flutes on the two facing single face webs are aligned, synchronized, and glued together flute tip-to-flute tip. The device for producing this type of double wall corrugated board is shown, for example, in U.S. Pat. No. 4,935,082. It has been suggested that such double wall corrugated board may be produced with a strength equivalent to conventional double wall board with an additional saving in paper by eliminating the intermediate liner web. However, the production of this modified double wall corrugated web is very slow by today's corrugating standards and cannot be produced at speeds greater than about 425 feet per minute (fpm).